1. Field of the Invention
The present invention relates to a device for generating synthetic smoke and also to a hazard detector tester utilising such a device.
2. Description of the Related Art
In the past, hazard detectors such as smoke detectors, have been tested by utilising an aerosol of fine particles dispensed from a pressurised can. One such tester is the one sold under the trade name ‘Trutest’ where an aerosol container is discharged into an intermediate chamber to accumulate the aerosol particles prior to delivering them through to the detector. However, the use of pressurized containers is not particularly convenient as they are classified as ‘hazardous’ and hence costly to transport. Also, the propellants used cause difficulty either because they are flammable, are greenhouse gases or attack the ozone layer. While it is possible to utilise suitable propellants and so overcome any environmental issues, there is a market for an alternative to the use of pressurized containers in certain circumstances.
It has previously been proposed in GB 2299005 to provide a device for vaporising liquids in order to produce synthetic smoke utilising an electrically heated heat exchanger. In this prior proposal, smoke-producing fluid which is to be vaporised is forced into a thin-walled metal tube by means of a pump, compressed air or gravity and the tube is connected to a source of current in order to directly heat the liquid in the tube.
A further proposal for generating synthetic smoke electrically is disclosed in U.S. Pat. No. 3,891,826 and utilises a capillary tube one end of which sits in a reservoir of liquid. Within the capillary tube is located a further tube and the gap between the outer wall of the further tube and the inner wall of the capillary tube creates an annular space which has capillary dimensions and which draws the liquid up into the annular space where it is heated by an electrically operated heated element housed within the further tube. This particular arrangement requires that there is a small head of liquid to feed into the capillary space. This renders it inappropriate for use in a device which might be tilted or inverted during use.